Epoxy resins have been used successfully in the formation of corrosion resistant maintenance-type coatings for years. These coatings have been applied from solvent solution using brush, roller of spray gun. Recent trends in environmental protection and health regulations have required that the solvents used for applying many types of coating agents must now be drastically reduced or eliminated. See, for example, Rule 442 of the Southern California Air Pollution Control District which replaces Rule 66 of the Los Angeles Air Pollution Control District.
Also, because of increased awareness of safety and health hazards, there is greater emphasis being placed on the toxicity of certain curing agents used in resin formulations. For example, the volatility of certain amines to cure epoxy resins under certain conditions create potential health hazards.
Films prepared from epoxy resins cured with amines are known; however, as noted, some amines present potential health hazards and the resulting films tend to exhibit excessive blushing; are slow to cure, i.e., take a long time to reach an acceptable degree of hardness; and are not readily useable in a water-borne system.
Most of these shortcomings can be partially eliminated by preparing an amine adduct with an epoxy resin. Thus, if excess amine is used to prepare the adduct, the resulting condensate can be used as an epoxy curing agent. When such amine-epoxy adducts are employed as epoxy curing agents the blushing and toxicity is reduced and the coating system has better handleability; however, these systems still have water sensitivity problems which tend to limit their use to organic solvent formulations.
It has now been found that faster curing times are possible as well as significantly reduced blushing and reduced toxicity is achieved when the epoxy curing agent is prepared in a two-step process using at least two different amines. More importantly, the resulting epoxy curing agent has decreased water sensitivity and is therefore useable in a water-borne system.